Now that filling your tank feels like you’re stuffing it full of ten-pound notes, we all want the best fuel economy we can get. There’s no shortage of advice on how to achieve this — whether it’s from websites or Dave down the pub — but unfortunately, it tends to be a mixture of solid information, overblown claims and downright fallacies. So in this two-part post, we’ll look at the best and worst fuel-saving tips.
This time, we’ll start off with three tips that either don’t work at all or won’t make any savings you’ll notice.
Tyre pressures — over-inflated claims
We’ve all heard that keeping your tyres at the right levels is essential for great fuel economy. Some of the claims of what this can achieve are pretty staggering. For example, tyre manufacturers GT Radial suggest that a drop of just 5psi could mean 10% greater fuel consumption. Great! If it’s true, then just a little vigilance could save you a hefty wodge of cash every year.
Unfortunately, we think that real-world results are unlikely to equal that. When Which? magazine tested a Peugeot 308, they found that deflating the tyres by a whopping 15 psi resulted in a modest 3% increase in fuel consumption. More authoritatively, the US Department of Energy (who ought to know what they’re talking about), estimate that each psi lost results in a 0.2% increase in fuel. Using their figures, a loss of 5psi tyre pressure increases fuel consumption by an unexciting 1%. That’s 1/10 of GT Radial’s estimate.
Don’t get us wrong, there are great reasons for keeping your tyres properly inflated. Running them radically below their recommended pressure is plain dangerous, eventually damaging the structural integrity of the tyre and making catastrophic failure a real possibility. Even moderate under-inflation will make your tyres wear more quickly. But when it comes to fuel economy, the effects of tyre pressure are a bit overblown.
Lose weight from your car for negligible savings
The single most prevalent and widely-believed fuel economy myth is the impact of removing weight from your car. The usual recommendation is to remove any accumulated junk and unnecessary tools. Now, whilst it’s technically correct that every single gram of unnecessary weight that you carry burns extra fuel, what’s always ignored is the issue of scale.
Yes, you will make considerable savings if you’re hauling around a spare Olympic barbell set, or your unnecessary tools include a concrete mixer. But for most people, clearing out their car is unlikely to yield any noticeable improvements in fuel economy.
A bit of maths makes the point. Let’s say you’re driving a family hatchback that weighs 1320kg. With a driver and passenger, the total might come to 1455kg. Concerned about your fuel economy, you clear out 5kg of sweet wrappers, kid’s toys, blankets and other detritus and another 5kg of tools. After all that effort, your car is now just 0.69% lighter. How much difference can that really make? About as much as it sounds.
A Canadian study estimated that for every 100kg of weight lost, drivers can save 0.3 litres per 100km. At current prices, that means that on a 88 mile return trip from Cardiff to Bristol, you’d save the grand sum of 52p. Remember, that’s for a 100kg reduction.
Our advice? If you want to save the pennies, you’d be better off concentrating on driving style (see Part Two).
Coasting along for increased fuel consumption
We’ve all heard this one, too: to save on fuel, slip the car into neutral when you’re going downhill. According to the theory, as the engine only idles in neutral, you’re saving fuel. This sounds pretty reasonable, but actually it’s mistaken: quite apart from being pretty dangerous, coasting in neutral is marginally more expensive.
Car and Driver does a good job of explaining why. Essentially the issue is to do with how the computer manages fuel injectors. If the car is coasting along in gear — in other words, you don’t have your foot on the accelerator — then the fuel injectors are shut down and you’re using no fuel. But this effect disappears when the car’s in neutral. The injectors open back up, and you start burning fuel again. Therefore, coasting in neutral actually costs more money.
Another thing: even if coasting in neutral worked how it was supposed to, the savings would probably be minuscule. As Popular Mechanics points out, at 30mpg, coasting in neutral down a mile-long hill (two minutes in neutral) would save you a piffling 0.033 gallons. And that’s assuming the car used no fuel at all at idle.
So coasting is neutral costs money, it increases wear on your brakes, and did we already mention it’s dangerous? Good, we’ll mention it again.
So what fuel economy tips do work?
Three nice easy fixes for your fuel economy, and none of them make a noticeable difference. Well, that’s a bit miserable then. Of course, it begs the question, ‘so what does work?’ Ah, we’re such teases. You’ll have to wait for Part Two for that. It will be here in a couple of weeks.